The recent widespread availability of tunable lasers has enhanced the interest in photochemical processes. The output of a carbon dioxide (CO.sub.2) infrared laser is resonant with the absorptions of a wide range of organic molecules, and because of this resonance, this type of gas laser has become the most popular for studies of infrared laser-induced chemical processes. The absorption of the laser radiation by the molecules promotes the molecules into excited vibrational states, and the molecules can become very reactive as a result.
In principle, the energy of the laser can be deposited into a single vibrational mode and the vibration can be excited to the point of dissociation. The resulting reactive species would be expected to react further. Such a process is referred to as a "mode-selective" laser-induced reaction. A mode-selective reaction requires that there be multiple photons deposited into the appropriate vibration over a short enough period of time so that the reaction can proceed before there is significant vibrational relaxation. This period of time is indeed short since energy relaxation within a given vibrational mode generally occurs on a time scale of picoseconds. For complex molecules there is also a redistribution of energy among different vibrational modes and rotational and translational levels. Furthermore, at pressures of a few torr and higher, intermolecular redistribution accompanies collisions. Consequently, it has been concluded that only a few microseconds are required for a molecule (which has been excited by an infrared laser) to reach a thermal equilibrium. Once the energy of the laser has been distributed throughout the molecule, any reaction which proceeds would very likely be similar to an ordinary pyrolysis reaction.
Even if the ultimate reactions are governed by thermal (or non-equilibrium thermal) processes, the laser-induced reactions will generally differ from ordinary pyrolytic thermal reactions because wall reactions are essentially eliminated from the former.
As noted hereinabove laser energy has been deposited to achieve a level of excitation to the point of dissociation of molecules to give reactive species. In experiments the laser energy has been distributed throughout the molecules to proceed along a reaction mode which is somewhat similar to an ordinary pyrolysis reaction.
This background information presented hereinabove hopefully provides the transitional language which focuses attention to another area to which laser-induced-chemistry has been found to be useful--not for producing a recoverable product formed from reactive species, but to the contrary, employing laser-induced-chemistry to achieve a means for eliminating toxic compounds from contaminated equipment or environment. The energetic species from a toxic compound could, for example, rearrange or react to form non-toxic species.
Of particular interest is a class of chemical agents known as nerve agents which constitute the most deadly toxins known to man. A slight exposure of some of these agents is sufficient to kill, with lethal doses as low as LD.sub.50 =10 .mu.g/kg. Further these nerve agents are extremely rapid in action. These two qualities of nerve agents make counteraction (detoxification) of these agents a particularly difficult problem. Decontamination is sometimes effected with alkaline solutions or bleach slurries which hydrolyze or otherwise chemically react with the agents. One is left with a noxious mixture to dissipate while the surface which has been decontaminated may have been damaged.
Since the chemical structures of some of the nerve agents contain an R--O--P linkage or specifically a C--O--P linkage, this linkage is of specific interest to this invention since the present invention relates to the decomposition of specific types of organophosphorus molecules containing the R--O--P linkage. A simple, efficient technique for decomposing (detoxifying) these molecules to relatively harmless compounds would be of tremendous value in decreased clean-up operations required for decontaminating equipment and environment. The problems of cleaning up equipment with corrosive chemicals increases hazards and primary costs as well as secondary costs, attributed to additional restorations required such as re-painting external surfaces of equipment, missiles, and fixtures would be obviated by the technique of this invention.
An object of this invention is to provide a laser photochemical method to effect decomposition of organophosphorus compounds containing the R--O--P moiety to thereby change these compounds to relatively harmless compounds.
A further object of this invention is to provide an efficient technique of detoxifying organophosphorus compounds wherein a continuous-wave, carbon dioxide laser is employed to decompose these compounds at a rate which is proportional to the level of the laser power employed.
Still a further object of this invention is to provide a laser photochemical method which serves as an efficient technique for detoxifying chemical agents containing the R--O--P linkage wherein as a result of lasers irradiation, the energy distibution cleaves a carbon-to-oxygen bond to yield relatively harmless compounds comprised of various alkanes and alkenes, and carbon dioxide as volatile products and a nonvolatile mixture of phosphates, phosphites, and polymeric phosphorus--containing compounds.